Abstract : We are interested in computationally sound implementations for languages of distributed communicating processes, with secure high-level primitives for authentication and secrecy, but without explicit cryptography. We develop such an implementation for a variant of the pi calculus [6]. In this language, security properties can be studied using traces and equivalences that account for the presence of an arbitrary (abstract) adversary that controls the network. The cryptographic implementation of the language uses standard primitives and assumptions; it guarantees that these abstract properties also hold in a concrete, distributed setting, against probabilistic polynomial-time active adversaries. At FCC'06, we intend to review and discuss the design space for programming languages with cryptographically sound implementations. In particular, we motivate some unusual design choices for our language, we discuss its current limitations, and we consider possible extensions.